This application is related to U.S. Pat. Application Ser. No. 07/358,688 filed May 30, 1989 and assigned to the same assignee as the present application.
This invention relates generally to batteries and more specifically to batteries which benefit from electrolyte circulation.
It has been known that in secondary batteries such as those typified by lead acid batteries using aqueous sulfuric acid or liquid electrolyte that the electrolyte tends to stratify when cycled due to varying densities. The stratification becomes aggravated during charge and recharge, affects cell performance and reduces battery life time. Additionally, ambient heat and efficient distribution of the internally generated heat are problems where the electrolyte is essentially stagnate.
The prior art is replete with examples of various devices used to circulate electrolyte in secondary batteries or otherwise prevent stratification. U.S. Pat. No. 916,320 issued on Mar. 23, 1909 to H.F. Joel illustrates a technique of tapering a center electrode relative to the separators such that the gas collecting on either side of the separator moves upward and accumulates in ever narrowing passageways, forcing electrolyte as bubbles up through orifices at the top and then over to the outside of the outer electrode where it moves downward. According to the patentee this draws the denser electrolyte from the bottom of the battery. U.S Pat. No. 2,584,117 issued on Feb. 5, 1952 to Elrod Jr. also recognized the problem and proposed the use of an air blown device to aerate the electrolyte to alter the density thereof to create circulation. Still another U.S. Pat. 4,283,467 issued Aug. 11, 1981 to Gutlich, et al. discloses a device that also utilizes gas to alter electrolyte density. U.S. Pat. No. 4,308,322 issued Dec. 29, 1981 to Hammar describes a pump within the battery comprising a gas collecting hood and passageways which utilize the generated gas to carry electrolyte as bubbles to the passageways, thus inducing circulation. Another design to reduce stratification is disclosed in U.S. Pat. 4,619,875 issued Oct. 28, 1986 to D.W. Stahura, et al. in which the separator has a plurality of laterally extending concave ribs on the surface thereof that act to trap the more dense electrolyte.
U.S. Pat. No. 529,199 issued Nov. 13, 1984 to Schoop provides several different embodiments of a device which serve to redistribute electrolyte in a battery. One particularly interesting embodiment involves the use of a planar member which forms a wall that is positioned adjacent and inside one of the back walls of a battery cell and extends across to each of the side walls thereof. The top side of the wall extends above the at-rest surface of the liquid electrolyte and terminates short of the cell base, providing an opening. When the electrolyte is disturbed by, for example, a sudden change of motion of the cell, the electrolyte fills the volume confined by the wall and the cell walls and forms a hydrostatic head. By gravity the head dissipates and the movement of electrolyte through the opening provides a beneficial circulation which equilibrates the undesirable temperature differentials and density gradients which otherwise forms during use in the electrolyte. To compensate for upward surge of electrolyte (which would effectively destroy the formation of the hydrostatic head and thus the beneficial currents), the patentee uses a one-way valve mechanism which closes the channel behind the wall to upward moving currents.
In the referenced co-pending application Ser. No. 07/358,688, incorporated by way of reference herein, it is demonstrated that the valve mechanism can be eliminated by making the average horizontal cross-sectional area of the mouth region, i.e., that portion of the volume enclosed by the wall and cell walls above the at-rest surface of the electrolyte, sufficiently greater than the average horizontal cross-sectional area of the throat volume. The upward surge of electrolyte dissipates before interfering with the formation of the hydrostatic head. The paramount advantage of the pump as described therein is the elimination of a moving part without reduction in effectiveness of the pump.
In some battery environments it would be desirable to have a pump which provides the same desirable result but which is separate from the walls of the cell. The foregoing addresses this situation as will be readily apparent from the ensuing description of a preferred embodiment of the invention.